DESCRIPTION: Metallothioneins are small, highly conserved, cysteine-rich proteins that bind a variety of metal ions. They are found in virtually all eukaryotic organisms and are believed to have an important role in heavy metal detoxifications and homeostasis. As expected with proteins that occupy such an essential physiological role, their expression is highly regulated. This regulation is achieved by the presence of multiple, distinct metallothionein genes, the predominant metallothionein gene is hMTIIA, which accounts for 50% of all metallothioneins expressed in cultured human cells. Because of its high constitutive expression level, coupled with its ability to be further induced by a large number of exogenous stimuli, the hMTIIA gene provides an ideal system for studies of regulation of gene expression in higher eukaryotic cells. The hMTIIA promoter is quite complex. In addition to cis-acting DNA sequences that serve as binding sites for trans-acting factors such as SP1, AP1, AP2, AP4, and the glucocorticoid receptor, the hMTIIA promoter contains eight consensus metal response element sequences. A zinc finger protein with a molecular weight of 120K (ZFP120) was cloned based on its ability to interact with the metal response element overlapping the hMTIIA transcription initiation site. In this proposal, the overall hypothesis is that the hMTIIA initiation sequence is a important regulatory element, and that ZFP120 is a key hMTIIA regulatory protein for basal and Metal-induced transcription. The long-term goal of this project is to understand the underlying mechanisms that regulated hMTIIA mRNA synthesis with particular emphasis on dissecting a novel cellular DNA-binding protein, ZFP120, that interacts selectively with an hMTIIA metal response element to regulate transcription. These studies will be of value not only in understanding the fundamentals of eukaryotic transcriptional regulation, but will also provide additional insights regarding the regulation of a physiologically important gene.